Outside of casino-specific rules, this follows the standard full minimum raise rule for big bet Holdem.
Legal raises (all-in) below the minimum are treated as calls, although players to act face a different bet size than previously. Therefore, a minimum raise by player D presumed to have more than 1200 chips behind, is 1200.
If player C were to go all-in for 1199 total, player D could make a legal non-all-in raise to 1200, and player E would still have the option to raise. This seems strange at first, but a raise here is practically the same as a call, both of which retain open action, so the difference is only a technical one. Furthermore, such a raise is seldom advantageous to the raiser, as it tends to offer favorable odds to players yet to act.
EDIT: I haven't found a "Holdem Rules" that outlines this interpretation with more specificity than "What is a minimum raise?" However, some time ago I wrote this logic into a poker engine and verified against existing poker sites, to answer the question: Does a raise over a non-minimum raise go on top of the new facing bet, or does it go on top of the last minimum-qualifying bet? The answer is the latter.